Salesforce Marketing Cloud (SFMC) runs on data : email addresses and phone numbers; first and last names; purchase history; cart information; product data; and more. Marketers take this data and use it to segment audiences (e.g. by age or gender or location), or personalization (e.g. "Hello FirstName") and for sending purposes. Data is also used to predict future behaviours. It is safe to say that data is SFMC's lifeblood.

All of this data needs to be fed into the product before it can be activated. But how? 4 key ways, each with its own use case and best practices.

1. One-time, low volume, manual imports

• Use .csv files for one-time imports
• Use case: Bringing in data related to webinar registrants, or booth sign-ups, for example.
• How does it work: Data from the .csv file is written into a data extension within SFMC.
• Data from the source .csv file is mapped to related fields in the target data extension. 
• Set-up: Data extension will need to be created prior to import.
• Best for: Bringing in low volume data (<20 MB). 

2. Large volume, one time or recurrent 

• Bring in large volumes of data by dropping files on FTP
• Use case: Bringing in large volumes of customer data from an external data warehouse / CRM / CDP
• How does it work: Csv (or zip files, which will be unzipped by the application) can be dropped onto an FTP site. An automation can be built to grab the contents of the files to write them into data extensions within SFMC.
• Set-up: FTP, automation, data extensions will have to be configured / created prior.
• Best for: Batch import of large volumes of near real-time data (both recurring and one time/ad-hoc). 

3. Integrate real-time data via API

• Integrate data from external websites, systems or apps via API.
• Use case: Bringing in real-time password reset requests made on an external website.
• How does it work: SOAP and REST APIs can be used to integrate SFMC with virtually any system.
• Set-up: Installed package (to generate API key (Client ID & secret)& data extension needs to be created. POST call needs to be made. Would require a technical skills.
• Best for: Integration of real-time data with external websites or apps which triggers a message (email, for example).

4. Integrate data from other Salesforce products

• Use an out of the box connector to integrate data from Sales Cloud, Community Cloud, Health Cloud etc.
• Use case: Integrate Salesforce CRM data with SFMC to send contacts and leads relevant messages.
• How does it work: Configure an out of the box connector to integrate the two systems. Integrated data can then be leveraged for marketing campaigns within SFMC.
• Set-up: Connector will need to be configured. An experienced architect may need to assist in the process. 
• Important: May impact contact counts (and/or impact billing), cause duplicate data. 

You may use more than one way to bring in data to your system. Some integrations may also be recurrent (e.g. via API or the Salesforce connector) while others may be one-time. As a best practice always work closely with a data architect who can help map out the architecture and integration patterns prior.